docs: def get_forum(self):
          """ Returns the considered forum. """
          pk = self.kwargs.get(self.forum_pk_url_kwarg, None)
          if not pk:  # pragma: no cover
              # This should never happen
              return
          if not hasattr(self, '_forum'):
              self._forum = get_object_or_404(Forum, pk=pk)
          return self._forum